Selective adsorption, flocculation, and fractionation of wood pulps with polyethyleneoxide

Abstract

It has been found that polyethyleneoxide (PEO) is selectively adsorbed onto and can flocculate unbleached kraft pulps, a soda pulp, and an unbleached sulfite pulp but not a bleached kraft pulp, a groundwood pulp, a thermomechanical pulp, or a neutral sulfite semichemical pulp. It is suggested that the flocculation mechanism is of the classical interparticle bridging type. Accordingly the flocculation was found to be sensitized by electrolytes or by decreasing the pH. It was also found that if an unbleached kraft pulp was methylated or acetylated no adsorption or flocculation with PEO takes place. On the basis of these experiments it is suggested that the primary adsorption sites on the unbleached kraft pulp are the phenolic lignin residues in the pulp, and that when the phenolic protons are replaced by acetyl or methyl groups, hydrogen bonding can no longer take place between the phenolic protons and the ether oxygens in the PEO. It is further shown that unbleached kraft pulps can be separated from bleached kraft pulps by utilizing this method of selective flocculation together with a microflotation procedure.